Variable inductances for tuned high-frequency circuits



Oct. 12, 1937; w. J. POLYDOROFF 2,095,420

VARIABLE INDUCTANCES FOR TUNED HIGH FREQUENCY CIRCUITS Filed Aug. 30, 1934 INVENTOR, Wan/Me JPOLYDOEOF/f BY 4 4 W ATTORNEY.

j v V 2,0 5,420 PATENT OFFICE vamam INDUCTANCES roa roman man-memos cmcurrs Whiliinir r. Polydoroii,

Johnson Laboratories,

poration oi Illinois C i ago, Ill. nor to Inc., Chicago, Ill, a cor- Applioa tion August so, less. Serial-No. 742,026

In Great Britain September}, 1983 This invention relates to variable inductances, and more particularly to variable inductances suitable for use in high-frequency resonant circuits, arranged to be adlusted to any' eq v within a relatively wide-band. Variable inductances of this type may be employed, for example, in broadcast receivers. 1 v

The variable inductances oi the present invention are of the type having compressed comminuted magnetic cores arranged to be movable relatively to the coils with which they are associated, the relative motion oi the coil and core producing changes in inductance which permit tuning the raonant circuit 01- which the inducttime may form a part, with or without the usual capacitance variation.

Variable inductance devices suitable for tuning resonant circuits over a range having a ratio oi maximum to minimum frequency 01' the order oi 3 are disclosed in myFrench Patent No. 737,154. The present specification is addressed .to cases in which it is desired-to tune one or more resonant circuits through a plurality oi frequency ranges which may be widely separated from one another medium and "long" wavelength ranges usually provided for in modern broadcast receivers) and additionally to cases in which it is desired to tune over a range oi frequencies greater in extent than can be covered bya simple variable so inductance device such as those described in my French patent above referred to.

It is one object of the present invention, therefore, to provide variable inductance devices capable of being varied through two distinct ranges oi inductance values. The maximum value of one be the same as the minimum value oi. or'they may be diiierent. Another object oi the-invention is to operatively link at least two windings by a unitary common core structure in such a manner-"that the mutual inductance between two windings is considerably varied in addition to the usual inductance variation.

The invention will be best understood by reierence-to the a'companying drawing in which Fig. 1 shows a variable inductancev device employing two coaxial coils diii'ering in sell-inductance value and a magnetic core. member movablerelatively to the coils: Fig. 2.-shows an arrangement in which two coils are placed side by side with their axes parallel, and the relatively movable core member consists of two cylindrical portions, preferably Joined by a magnetic yoke; Fig. 3 55 shows an arrangement in which the two coils are concentric, one coil being cylindrical and the other tapered in' form, the core member being shaped to adapt it to the coils; and Fig. 4 shows an arrangement in which a cylindrical coil and o a tapered are arranged side by side, the

'2 Claims. (01. 171-242) core consisting of separate members adapted to cooperate with the coils.

Magnetic core materials and cores suitable for use in the construction of the variable inductances of the present invention are disclosed in my U.'B. Patents Nos. 1,940,228 and 1,982,689; In general, the cores consist oi very flnely divided magnetic material, such as pure iron, the particles being 01' such size as to reduce the losses in the resultant cores to a suitable minimum. The particles are individually insulated with a suitable insulator and are then molded into compressed bodies of suitable shape by the employment oi an appropriate plastic binding material, sumcient pressure being used in the molding to give the resultant cores the desired value oi apparent permeability.

Circuit arrangements in which variable inductance devices or the types herein contem plated may be advantageously employed are described in my French Patents Nos. 737,154 and According to the present invention, two separate coils or windingsare associated with a single magnetic core unit, which is movable relatively to the coils. The movement may be so arranged that the core influences both coils simultaneously or it may be arranged in such a manner that the core influences either winding at will. In either arrangement the inductances oi the two windings are controlled by the relative movement of the single core unit.

In thev embodiments shown in Figs. 1 and 2, the two coils or windings I, 2 are wound on two cylindrical forms 3, 4 oi the same dimensions, although one coil may be oi greater diameter than the other if required. In the arrangement shown in Fig.1 the two coils I, 2 are mounted eoaxially on any suitable support. The core member l is cylindrical in shapeand is to be moved progremively through the coils. It will be understood that the two coilsmay be so connected relatively to each other that they will be either additive or subtractive in inductance value. As will be seen from the drawing, however, in order to secure the advantages of the invention, the windings are so wound and connected that current flow in one 01' the windings is in opposite angular sense to current flow in the other winding. As disclosed in my French Patent No. 771,898, the coils may be connected to appropriate switching means, which may be automatically operated by the Additionally, the switching means may be arranged to connect the two coils in series or in parallel and to change the directional the windings' from an additive to a subtractive relation or vice versa. By proper choice of the switching arrangement employed and by appropriate design of the coils themselves, variation" throughout twoor more different frequency ranges, each havin a ratio of maximum to minimum -frequency of the order of 3 to 1, may be readily accomplished.

In theembodiment illustrated in Fig. 2 the two coils I, 2 are mounted side by side with their axes parallel. The core member 6 differs from that illustrated in Fig. 1 in that it consists of two cylindrical members I, 8 and a yoke member 9. The coils l, 2 are securely supported by any suitable'means and the core unit is arranged to be moved in such a manner that the core member I may be moved into and out of coil I while the coremember 8 moves into and out of coil 2.

Similarly to the arrangement shown in Fig. 1, the coils of Fig. 2 may be connected to appropriate switching means to accomplish changes in inductances to produce variation throughout two or more different frequency bands.

In Fig. 3 the coil Illa is wound on a cylindrical form, whereas the coil I0 is wound on a tapered form, the coils "la, l0 being coaxially mounted on a suitable support, such as a plate. The core member I l consists of two portions l2 and iii, the portion l2 being of tubular form and of such dimensions as to influence the inductance .of coil Illa directly, whereas the portion I3 is conical in shape and is arranged to influence the inductance of the coil Ill directly. The two portions l2 and- I3 of the core unit Il may be separately molded and mechanically joined in such a manner that they are intimately associated magnetically at one end, or the entire core member H may be molded in one piece. The arrangement of this Figure is particularly useful when the larger diameter winding We is used for shortwave tuning.

In the embodiment shown in Fig. 4, the coil I4 is cylindrical whereas the coil I5 is conical in shape, the two coils being mounted'side by side with their axes parallel on any suitable support. The core member I6 is cylindrical in shape and is arranged to directly influence the inductance of the coil M. The core member ll consists of two portions l8, IS, the member l8 being conical in shape and adapted to be moved into [5, the member l9 being tubular in shape and arranged to move outside the coil IS in such a manner as to substantially surround the coil l5 when fully advanced. The members l8'and l9 may be joined by a separate magnetic yoke 20 or the yoke 20 may be molded as part of the internal core member 18 or a partof the external core member l9. Alternatively, the entire core I'I consisting of the portions l8, I9, 20 may be molded in one piece. In Figs. 2 and 4 the smaller inductance coil alone operates over the high-frequency range, the other part of the core providing a low-reluctancepath for the return flux, thus increasing the range. When the higher inductance coil is switched into 'series relation with the first coil, both cores also act to increasev the inductance variation.

In the arrangement of Figs. 2 and 4, the two coils (I, 2 in Fig. 2 and M, IS in Fig. 4) are so connected that the fluxes in the two coils will be in opposite directions at any instant. Thus practically all the flux from one end oi one coil enters the adjacent end of the other coil, the arrangement being what is commonly known as a binocular pair. It will be noted that the arrangement is such that current flow in one of 'the'windings is in opposite angular sense to current flow in movement which have been the coil variation in the inductance of the device with the 1 two coils connected in series and additively related, may be secured.

It will be observed that the coils have been shown as single-layersolenoidal windings, since this produces minimum high-frequency resistance in the winding itself; but, where high inductance values are required, multiple-layer windings, pref erably bank-wound, may be employed.

It is preferable to use a conductor consisting of several insulated strands, commonly known as Litz wire, for the windings, although, of course, a solid conductor may be used if desired. In practical embodiments of the invention it will frequently be found convenient to make one of the coils single-layer solenoidal with spaced turns for the higher frequency range, and the other coil a multiple-layer winding for the lower frequency range.

For securing the relative movement between the coils and the core unit, any suitable mechanical drive may be employed. Forms of mechanical found to be suitable are described in my French Patent No. 737,154.

It will be understood that any of the arrangements herein described may employed in" the construction of a band-pass filter or other tuning system in which two oscillatory circuits are tuned simultaneously through two diflerent ranges of frequency and in which some inductive coupling between the two oscillatory circuits is permissible or desirable. It will also be understood that plural inductance devices of types herei in disclosed may be arranged to time a plurality of circuits through two or more frequency ranges.

1 In such embodiments the mechanical drive will what I tance value and whose effective inductance is varied by said core structure, and switching means to alter the connections of said windings, said core structure constituting a common magnetic path or said windings to increase the total effective inductance varlatio and said windings being arranged coaidally end to end and magnetically in opposed relation.

2; A variable inductance device for multirange tuning, including a comminuted magnetic core structure, two windings of diflerent selfinductance value and whose eflective inductance is varied by said core structure, said windings being arranged coaxially end to end'and magnetically in opposed relation, and switching means to alter the connections of said windings, said core structure constituting a common magnetic path for said windings to increase the total effective inductance variation and being arranged to move into one of said windings and out of the other of said windings simultaneously.

WLADDHR J. 

